The present disclosure relates to a transparent conductive electrode and a method of forming the same. More particularly, the present disclosure relates to a transparent conductive electrode stack which includes at least a layer of a carbon-containing material, an organic light emitting diode (OLED) device that includes the transparent conductive electrode stack, and methods of forming the transparent conductive electrode stack and the OLED device containing the same.
Organic light emitting diode device technology is emerging as a leading technology for displays and lighting. OLED displays posses key advantages including vibrant color, high contrast ratios, wide viewing angles and are flexible over conventional liquid crystal displays (LCDs). Moreover, OLED lighting is much more efficient than incandescent bulbs and has similar efficiency as the nitride based light emitting diodes (LEDs).
A typical OLED comprises a substrate which is usually made of glass or a similar transparent material. An anode layer is positioned on the substrate. The anode layer can be made of a material having a relatively high work function and is substantially transparent for visible light. A typical material for the anode layer is indium tin oxide (ITO). A layer of electroluminescent material is positioned on the anode layer, serving as the emitting layer of the OLED. Common materials for forming the emitting layer are polymers such as, for example, poly(p-phenylenvinylene) (PPV) and molecules like tris(8-oxychinolinato) aluminum (Alq3). In the case of molecules, the emitting layer typically comprises several layers of the molecules. A cathode layer of material having a lower work function like aluminum (Al), calcium (Ca) or magnesium (Mg) is positioned on the emitting layer. During operation of the OLED, the cathode layer and the anode layer are connected to a power supply.
The basic principles of electroluminescence and, thus, of the OLED are the following: The anode layer and the cathode layer inject charge carriers, i.e., electrons and holes, into the emitting layer. In the emitting layer, the charge carriers are transported and the charge carriers of opposite charge form so called excitons, i.e., excited states. The excitons decay radiatively into the ground state by generating light. The generated light is then emitted by the OLED through the anode layer which is made of transparent material like ITO. The color of the generated light depends on the material used for the organic emitting layer.